Systems and methods for operation of a flexible fuel combustor

ABSTRACT

The present disclosure relates to systems and methods that are useful for controlling one or more aspects of a power production plant. More particularly, the disclosure relates to power production plants and methods of carrying out a power production method utilizing different fuel chemistries. Combustion of the different fuel mixtures can be controlled so that a defined set of combustion characteristics remains substantially constant across a range of different fuel chemistries.

RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication No. 62/467,924, filed Mar. 7, 2017, the disclosure of whichis incorporated herein by reference.

FIELD OF THE DISCLOSURE

The presently disclosed subject matter relates to systems and methodsfor operation of one or more components of a power generating system.More particularly, the present disclosure relates to operation of acombustor so that different types of fuels may be combusted in the samecombustor under one or more sets of conditions.

BACKGROUND

As the demand for electrical power production increases there is acontinuing need for power production plants to meet such needs. Becauseof market demands, it is desirable for such power production to beachieved with the greatest possible efficiency; however, growingrequirements for carbon capture have required technological advances.For example, U.S. Pat. No. 8,596,075 to Allam et al., the disclosure ofwhich is incorporated herein by reference, provides for desirableefficiencies in oxy-fuel combustion systems utilizing a recycle CO₂stream wherein the CO₂ is captured as a relatively pure stream at highpressure. Although many known power producing systems are configured forcombustion of a specific type of fuel (e.g., natural gas versus syngas),power producing facilities can be even further improved by allowing foroperation with different types or sources of fuels without requiringsignificant changes to the necessary components of the power producingfacility, such as the combustor that is used. Accordingly, there remainsa need in the art for further means for operation of a power productionplant such that different fuels may be utilized without significantchanges in the underlying equipment used to carry out the powerproduction process.

SUMMARY OF THE DISCLOSURE

The present disclosure provides systems and methods for powerproduction. More particularly, the present disclosure provides operatingconditions whereby a power production system can accommodate differentfuels without a requirement for significant modifications to a combustorthat is utilized in carrying out the power production process. This canprovide a significant advantage since different fuels can be switched asneeded without the requirement for associated swapping of parts for thepower production system.

The properties (including combustion properties) of different fuelsources that may be used in a power production method according to thepresent disclosure can differ significantly. For example, the fuelproperties of natural gas are significantly different from the fuelproperties of a synthesis gas (“syngas”). Likewise, the properties ofboth natural gas and syngas can differ significantly from the propertiesof substantially pure methane. As one example, the heating value ofnatural gas is approximately five times higher than the heating value ofdried syngas taken from a coal gasifier. As another example, hydrogenalso has significantly different properties when compared to naturalgas, substantially pure methane, and/or syngas. Therefore, for a givenmass of each fuel, properties such as flame characteristics, thermalenergy delivered to the downstream system temperature profiles, exhaustgas conditions, and exhaust gas compositions will vary significantly. Acombustor for a power production facility must be designed as a fixedchamber that is customized to the properties of the fuel that will becombusted therein in order to optimize combustor performance. As such,only a narrow range of fuel mixtures can be matched with the combustordesign conditions (and therefore flame and combustor outlet conditions)and thus be tolerable for use in the combustor. Further, mixtures withinthis range may still cause perturbations in combustor or flame behaviorthat must be tightly controlled.

In one or more embodiments, the present disclosure provides systems andmethods whereby a power production plant can be closely controlled inrelation to combustion properties even when utilizing different fuelstypes and/or fuel mixtures. In some embodiments, the present inventionthus can relate to a power production plant comprising: a combustorconfigured to receive a fuel, an oxidant, and a diluent, the combustorbeing adapted to combust different fuel compositions; a turbine; agenerator; a supply system for the fuel; a supply system for theoxidant; and a control system configured to adjust one or moreparameters related to one or more of the fuel, the oxidant, and thediluent such that combustion characteristics are maintained within adefined set of operation parameters for all of the different fuelcompositions. In the present systems, the control system in particularcan be critical to achieving the necessary system performance.

In one or more embodiments, the present invention further can relate toa method of power production, the method comprising: delivering anoxidant to a combustor; delivering a diluent to the combustor;delivering a fuel to the combustor, the fuel being a mixture ofmaterials that varies over the course of the power production method;passing a combustion product stream from the combustor through a turbineto generate power; and controlling one or more parameters related to oneor more of the fuel, the oxidant, and the diluent such that combustioncharacteristics are maintained within a defined set of operationparameters for different mixtures of materials forming the fuel.

In some embodiments, control methods can include blending of twodifferent fuels to normalize combustion of one of the fuels that may besubject to fluctuation of composition. Such blending likewise can beutilized to provide for a smooth transition between the use of the twodifferent fuels using the same combustor. As a non-limiting example fornormalizing combustion of a fluctuating syngas composition, a dilutednatural gas fuel or a substantially pure CO₂ stream can be utilized as atuning factor to adjust the characteristics of the syngas fuel so it isnormalized to be close to the intended fuel characteristic design pointby blending the diluted natural gas fuel or the CO₂ diluent stream withthe syngas fuel at a proper mixing ratio. As noted, this can beparticularly useful when the syngas coming into the combustorexperiences fluctuation or the syngas composition significantly deviatesfrom the design point because of being derived from differentgasification systems. In some embodiments, it can be particularly usefulto maintain the concentration of the diluent entering the combustor tobe higher than the concentration of oxygen and/or fuel entering thecombustion chamber. Having a diluent flow than is significantly largerthan the oxygen flow and/or the fuel flow into the combustor can providefor a very stable combustion environment while simultaneously allowingfor perturbations and/or variations of the fuel chemistry.

Additionally, combustor outlet conditions can be maintained regardlessof the type of fuel being used. This can be achieved, for example, bymodulation of the flow rate of the diluent injection section downstreamof the diffusion flame zone section. Outlet temperature can bemaintained by adjusting the mass flow rate of the diluent injection atthis section. The mass flow rate of the diluent in this section willalso be significantly greater than the combined flowrate of the fuel andoxidant. Moreover, by keeping the diluent flow ratio large relative tothe oxygen flow and/or the fuel flow into the combustor, the combustorexit composition can be substantially stable across a variety of fuelchemistries.

In some embodiments, the present disclosure specifically can provide amethod for normalizing combustion in a power production process. Inexemplary embodiments, the method can comprise: providing a variablefuel to a combustor, the variable fuel having a composition that variesduring operation of the power production process; combusting thevariable fuel in the combustor with an oxidant to provide a combustorexhaust stream; passing the combustor exhaust stream through a turbineto generate power; and implementing at least one control function suchthat at least one combustion property (e.g., one or both of atemperature and a mass flow of the combustor exhaust stream exiting thecombustor) varies by no greater than 10% as the composition of thevariable fuel varies during operation of the power production process.In further embodiments, the method may be further defined in relation toone or more of the following statements, which may be combined in anynumber and order.

The variable fuel can be a syngas, and a ratio of carbon monoxide tohydrogen in the syngas can vary during operation of the power productionprocess.

The variable fuel can be a mixture of methane, carbon monoxide, andhydrogen, and a ratio between the methane, carbon monoxide, and hydrogencan vary during operation of the power production process.

The oxidant can be a mixture of oxygen and a diluent (e.g., an inertgas, carbon dioxide, or water).

The oxidant can include about 5% to about 50% by mass oxygen, with theremaining portion of the oxidant being the diluent.

The oxidant can include about 15% to about 30% by mass oxygen, with theremaining portion of the oxidant being the diluent.

The at least one control function can include varying a ratio of theoxygen to the carbon dioxide in the oxidant as the composition of thevariable fuel varies during operation of the power production process.

The at least one control function can include varying one or more of atemperature of the oxidant input to the combustor, a temperature of thevariable fuel input to the combustor, a flow rate of the oxidant inputto the combustor, and a flow rate of the variable fuel input to thecombustor as the composition of the variable fuel varies duringoperation of the power production process.

The variable fuel provided to the combustor can be blended with anormalizing fuel having a substantially constant composition.

The normalizing fuel can be natural gas or substantially pure methane.

The at least one control function can include varying a ratio of thenormalizing fuel to the variable fuel that is combusted in thecombustor.

The variable fuel provided to the combustor can be blended with adiluent.

The diluent can be an inert gas.

The diluent can be carbon dioxide.

The diluent can be water.

The at least one control function can include varying a ratio of thediluent to the variable fuel that is combusted in the combustor.

The combustor can be configured with a combustion zone and a dilutionzone, wherein the combustion zone can be upstream of the dilution zone,and the dilution zone can be downstream of the combustion zone, and adiluent can be injected into the combustor in the dilution zone.

A ratio of the length of the combustion zone to a length of the dilutionzone can be about 0.1 to about 10, about 0.2 to about 5, or about 0.25to 1.0.

The at least one control function can include: controlling a mass flowrate of the diluent injected into the combustor in the dilution zone tobe greater than a mass flow rate of the variable fuel provided to thecombustor; controlling a mass flow rate of the diluent injected into thecombustor in the dilution zone to be greater than a mass flow rate ofthe oxidant provided to the combustor; or controlling a mass flow rateof the diluent injected into the combustor in the dilution zone to begreater than a mass flow rate of both of the variable fuel provided tothe combustor and the oxidant provided to the combustor.

The at least one control function can include varying one or more of atemperature, a flow rate, and a chemistry of the diluent injected intothe combustor in the dilution zone as the composition of the variablefuel varies during operation of the power production process.

The diluent can be an inert gas.

The diluent can be carbon dioxide.

The diluent can be water.

In some embodiments, the present disclosure further can relate to apower production plant. For example, such power production plant cancomprise: a combustor configured to receive an oxidant, a diluent, and avariable fuel having a composition that varies during operation of thepower production plant, the combustor being configured to output acombustor exhaust stream; a turbine; a generator; a supply system forthe variable fuel; a supply system for the oxidant; and a control systemconfigured to adjust one or more parameters related to one or more ofthe variable fuel, the oxidant, and the diluent such that at least onecombustion property (e.g., one or both of a temperature and a mass flowof the combustor exhaust stream exiting the combustor) varies by nogreater than 10% as the composition of the variable fuel varies duringoperation of the power production plant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a power production plant and associatedmethod of operation thereof according to embodiments of the presentdisclosure; and

FIG. 2 is schematic illustration of a combustor suitable for useaccording to embodiments of the present disclosure

DETAILED DESCRIPTION

The present subject matter will now be described more fully hereinafterwith reference to exemplary embodiments thereof. These exemplaryembodiments are described so that this disclosure will be thorough andcomplete, and will fully convey the scope of the subject matter to thoseskilled in the art. Indeed, the subject matter can be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will satisfy applicable legal requirements. As usedin the specification, and in the appended claims, the singular forms“a”, “an”, “the”, include plural referents unless the context clearlydictates otherwise.

The present disclosure relates to systems and methods adapted forcontrolling the operation of a power production plant. As such, thepresent disclosure further relates to power production plants includinga variety of elements, including such control functions. Non-limitingexamples of elements that may be included in a power production plant(and method of operation thereof) according to the present disclosureare described in U.S. Pat. Nos. 8,596,075, 8,776,532, 8,869,889,8,959,887, 8,986,002, 9,062,608, 9,068,743, 9,410,481, 9,416,728, U.S.Pat. Pub. No. 2010/0300063, U.S. Pat. Pub. No. 2012/0067054, U.S. Pat.Pub. No. 2012/0237881, and U.S. Pat. Pub. No. 2013/0213049, thedisclosures of which are incorporated herein by reference.

An exemplary power production plant 100 for carrying out a powerproduction process according to the present disclosure is illustrated inFIG. 1. As seen therein, a combustor 120 is configured for receipt ofone or more fuels, an oxidant, and a diluent. More particularly, an airstream 101 can pass through an air separation unit 102 to provide anoxidant stream 103 that passes to the combustor 120. The air separationunit 102 can include the necessary compression equipment to provide theoxidant at the desired pressure, or a separate compressor may beprovided in-line between the air separation unit 102 and the combustor120. In such instance, a first portion 183 a of the recycled carbondioxide stream 184 can be mixed with the oxidant stream 103 prior tocompression. A first fuel stream 107 a and an optional second fuelstream 107 b can be passed through a compressor 108 to form a compressedfuel stream 109 that is passed to the combustor 120. A recycled carbondioxide stream 184 is likewise passed to the combustor 120 and canfunction as a diluent stream. In some embodiments, a first portion 183 aof the recycled carbon dioxide stream 184 can be withdrawn and combinedwith the oxidant stream 103 to form a diluted oxidant stream having anO₂/CO₂ ratio as otherwise described herein. Likewise, in someembodiments, a second portion 183 b of the recycled carbon dioxidestream 184 can be withdrawn and combined with the fuel stream 109 toform a diluted fuel stream having a fuel/CO₂ ratio as otherwisedescribed herein. Although a single compressor 108 is illustrated, it isunderstood that a plurality of compressors may be used, and a separatecompressor may be used for each of the fuel streams that is used.Likewise, although the second portion 183 b of the recycled carbondioxide stream 184 is shown as being added to the fuel stream 109, it isunderstood that the diluent may be added to one or both of the fuelstreams prior to compression. Additionally, the diluent for use with thefuel and the oxidant is not limited to the recycled carbon dioxidestream 184. Rather, the diluent may be taken from any one or more ofstreams 155, 165, 171, 177, 182, and 184.

A combustor exhaust stream 130 is passed through a turbine 135 where itis expanded to produce power in generator 136. A turbine exhaust stream137 is passed through a heat exchanger 140 where it is cooled to formstream 142, which is further cooled to near ambient temperature in acooler 144. The cooled turbine exhaust stream 146 is then processed in awater separator 150 to provide a water stream 152 and a substantiallypure carbon dioxide stream 155, which is compressed in a compressor 160to form an intermediate compressed stream 165. The intermediatecompressed stream 165 is cooled in a cooler 170 to increase the densityof the carbon dioxide and form an increased density carbon dioxidestream 171, which is pumped in pump 175 to a high pressure for input tothe combustor 120. A carbon dioxide product stream 180 can be withdrawnfrom the high pressure carbon dioxide stream 177 to leave a carbondioxide recycle stream 182 that is passed back though the heat exchanger140 to be heated against the turbine exhaust stream 137. The heatedrecycle carbon dioxide stream 184 is then routed back to the combustor120 for use as a diluent.

A power production plant according to the present disclosureparticularly can be configured for specific control of the combustionstep of the power production process. As such, a controller 190 can beincluded in the power production plant 100, and the controller can beconfigured to provide one or more outputs 191 that implement one or morecontrol functions that adjust operation of the combustor 120 toaccommodate a variable fuel. The outputs 191, for example, may provideinstructions to one or more components of the power production plant100, such as various valves, pumps, or the like that can be effective toadjust flow of one or more streams. Likewise, the controller 190 mayreceive one or more inputs 192, such as from a sensor, that can providedata specifically related the variable chemistry of the variable fuelthat can be used to determine when further control functions asdescribed herein should be implemented to adjust one or more combustionproperties and maintain a substantially consistent combustion profile.

As used herein, a “variable fuel” is understood to mean a fuel having acomposition that varies during operation of the power productionprocess. Because the present disclosure utilizes a variable fuel, it isnot necessary to maintain a substantially constant fuel compositionduring operation. Rather, the composition of the fuel can change withoutsubstantially interruption to the operation of the power productionplant. For example, where the variable fuel is a syngas, a ratio ofcarbon monoxide to hydrogen in the syngas can vary. For example, thecarbon monoxide to hydrogen ratio in the syngas can vary from about 0.8to about 3.0, from about 0.85 to about 2.8, or about 0.9 to about 2.6during operation of the power production process without requiringsignificant interruption of the process and without requiring changes incombustion equipment. As another non-limiting example, the variable fuelcan be a mixture of methane, carbon monoxide, and hydrogen, and a ratiobetween the methane, carbon monoxide, and hydrogen can vary duringoperation of the power production process without requiring significantinterruption of the process and without requiring changes in combustionequipment. Likewise, the presently disclosed configurations allow forsignificant changes in the nature of the fuel. For example, the variablefuel can vary in macro composition (i.e., the chemical makeup of thematerial) as opposed to micro composition (i.e., the ratio of componentsof the fuel). A variance in the macro composition can comprise changingbetween utilizing syngas and instead utilizing natural gas or changingbetween utilizing natural gas and instead utilizing hydrogen.

The advantages of the present disclosure can be realized through theimplementation of defined controls over the operation of the combustor.As noted above, a power production process can comprise combusting avariable fuel in a combustor in the presence of a content of a diluent(preferably CO₂) and a content of an oxidant (preferably substantiallypure O₂). As such, all three of the variable fuel, the diluent, and theoxidant will be input to the combustor. Preferably, the variable fueland the oxidant are input in a substantially stoichiometric ratio(although an excess of oxidant in the range of about 0.1% to about 5%,about 0.25% to about 4%, about 0.5% to about 3%, or about 1% to about 2%molar can be provided to ensure substantially complete combustion of allfuel input to the combustor). Any one or more of the variable fuel, thediluent, and the oxidant can be input to the combustor in asubstantially pure state (i.e., not mixed with a further material).Alternatively, the variable fuel, the diluent, and/or the oxidant can beinput to the combustor in any combinations (i.e., a mixture of thevariable fuel and the diluent and/or a mixture of the diluent and theoxidant). One or more characteristics of the combustion can becontrolled through varying one or more characteristics of the streamsbeing input to the combustor. Thus, the variable fuel that is subject tohaving varying fuel chemistries can be utilized without requirement ofsignificant changes to the system components despite the fuel chemistrychanges.

Use of a diluent particularly can be beneficial for controlling variousparameters of the combustion process. A diluent may be mixed with avariable fuel and/or a normalizing fuel, and/or an oxidant, and/or acombustion product. Substantially pure carbon dioxide particularly maybe used as a diluent. An inert gas may be used as a diluent. Water(e.g., steam) may be used as a diluent. The diluent may be a mixture ofmaterials (e.g., carbon dioxide and water). The same diluent may be usedfor mixture with any of the variable fuel, the normalizing fuel, theoxidant, and the combustion product. Alternatively, two or moredifferent diluents may be used for mixture with any of the notedstreams.

In one or more embodiments, any one or more of the pressure of thecombustor exhaust stream, the temperature of the combustor exhauststream, and the chemistry of the combustor exhaust stream can becontrolled to be maintained within defined parameters without the needfor re-configurations of the combustor despite changes in the chemistryof the variable fuel. For example, the combustor exhaust stream can havea pressure in the range of about 150 bar to about 500 bar, about 200 barto about 400 bar, or about 250 bar to about 350 bar. The temperature ofthe combustor exhaust stream can be in the range of about 700° C. toabout 1500° C., about 900° C. to about 1400° C., or about 1000° C. toabout 1300° C.

In some embodiments, the present disclosure thus can provide methods fornormalizing combustion in a power production process utilizing avariable fuel. For example, such methods can comprise providing thevariable fuel to the combustor, combusting the variable fuel in thecombustor with an oxidant to provide a combustor exhaust stream, passingthe combustor exhaust stream through a turbine to generate power, andimplementing at least one control function such that one or morecharacteristics of the combustor exhaust stream exiting the combustorremains controlled within a defined range despite the variance in thechemistry of the fuel during operation of the power production process.For example, in some embodiments, the control function can be configuredsuch that a temperature of the combustor exhaust stream exiting thecombustor varies by no greater than 40%, no greater than 20%, no greaterthan 15%, no greater than 10%, no greater than 8%, no greater than 6%,no greater than 4%, no greater than 2%, or no greater than 1% as thecomposition of the variable fuel varies during operation of the powerproduction process.

In some embodiments, the diluent can be added to the variable fueland/or oxidant stream to control other parameters which are important tothe operation of the combustor. As a non-limiting example, the jet speedof the variable fuel passing through the fuel injection nozzles can bemodified by changing the rate of addition of the diluent to the fuelstream.

The ability to control combustion and enable the utilization of avariable fuel is further evident in relation to the combustorillustrated in FIG. 2. In one or more embodiments, combustion can benormalized despite variances in combustion characteristics arising fromthe differing chemistries of the variable fuel. This can be achieved,for example, by adjusting one or more characteristics of one or more ofthe streams input to the combustor. As such, a single combustor can beused for combustion of a variety of different syngas compositions aswell as combustion of a variety of different gaseous fuels, such asnatural gas, substantially pure methane, hydrogen, or the like.Normalization of combustion can be quantified, for example, in terms ofany one or more of fuel heating value, flame temperature, combustionpressure, combustor exit temperature, mass flow out of the combustor,turbine inlet flow chemistry, turbine speed, and other such variables.In some embodiments, for example, the actual heating value achieved inthe combustor can differ from the theoretical heating value based on thegiven fuel chemistry due to a normalizing function as otherwisedescribed herein. In exemplary embodiments, a defined heating valuerange can be set for combustor operation, and the defined heating valuerange can be maintained even though the actual heating value of thevariable fuel may increase above the defined heating value range and/orthe actual heating value of the variable fuel may decrease below thedefine heating value range during the course of operation of the powerproduction process. Specifically, the normalizing function can beeffective to maintain the heating value in the combustor within 40%,within 20%, within 15%, within 10%, within 5%, within 2%, or within 1%of a predetermined value despite changes in the fuel chemistry of thevariable fuel. In other words, the heating value of the combusted fuelin the combustor may vary by no more than the above-noted values duringoperation of the power production process

In some embodiments, the flame temperature in the combustor and/or thecombustor exhaust stream exit temperature can be maintained within adefined range (which can be less than what would be expected based uponthe given fuel chemistry or greater than what would be expected basedupon the given fuel chemistry) by implementing one or more of thenormalizing functions described herein. In exemplary embodiments, adefined flame temperature in the combustor and/or a defined exittemperature for the combustor exhaust stream can be set for combustoroperation, and the defined temperature can be maintained even thoughchanges in the fuel chemistry of the variable fuel would be expected tosignificantly change the temperature. Specifically, the normalizingfunction can be effective to maintain the defined flame temperature inthe combustor and/or the defined exit temperature for the combustorexhaust stream within 40%, within 20%, within 15%, within 10%, within5%, within 2%, or within 1% of the defined temperature. In other words,the flame temperature in the combustor and/or the exit temperature forthe combustor exhaust stream may vary by no more than the above-notedvalues during operation of the power production process.

In some embodiments, the mass flow of the combustor exhaust streamexiting the combustor can be maintained within a defined range byimplementing one or more of the normalizing functions described herein.In exemplary embodiments, a mass flow rate of the combustor exhauststream exiting the combustor (or a mass flow range) can be set forcombustor operation, and the defined mass flow rate (or mass flow range)can be maintained even though changes in the fuel chemistry of thevariable fuel would be expected to significantly change the mass flow.Specifically, the normalizing function can be effective to maintain thedefined mass flow of the exhaust stream exiting the combustor within40%, within 20%, within 15%, within 10%, within 5%, within 2%, or within1% of the defined mass flow. In other words, the mass flow for thecombustor exhaust stream exiting the combustor may vary by no more thanthe above-noted values during operation of the power production process.

In one or more embodiments, the varying chemistries of the variable fuel207 a being input to the combustor 220 can be normalized by beingblended with a diluent 283 b which, in preferred embodiments, cancomprise substantially pure carbon dioxide. The diluent 283 b can thencontrolled as a normalizing function that can be adjusted in one or moremanners as the fuel chemistry of the variable fuel 207 a changes duringoperation of the power production process. Controlling this function canbe effective to cause the flame generated in a combustion zone 221 ofthe combustor 220 by the combustion of the variable fuel 207 a blendedwith the diluent 283 b can be substantially unchanged regardless of theactual chemistry of the variable fuel that is utilized for combustion.In some embodiments, the control function imparted by blending thediluent with the variable fuel can be based upon any one or more of thefollowing:

The dilution ratio of the diluent blended with the variable fuel priorto combustion: The dilution ratio can vary based upon the actual heatingvalue of the variable fuel at the time of dilution. For example, whenthe chemistry of the variable fuel provides a relatively low heatingvalue, the dilution ratio (i.e., the amount of diluent added) can below, and when the chemistry of the variable fuel provides a relativelyhigh heating value, the dilution ratio can be higher. In this manner, anaverage heating value can be achieved. In some embodiments, the ratio ofdiluent to variable fuel can be about 0.1 to about 2, about 0.5 to about1.5, or about 0.8 to about 1.2.

The temperature of the diluent when added to the variable fuel: Thetemperature of the diluent can be used, for example, to control theflame temperature in the combustor. For example, when the chemistry ofthe variable fuel provides a relatively low heating value, the diluentcan be provided at a higher temperature so as not to artificially lowerflame temperature. When the chemistry of the variable fuel provides arelatively high heating value, however, the temperature of the diluentcan be lower so that the flame temperature does not exceed a desiredrange. The temperature of the diluent when added to the variable fuelcan be effective to change the overall temperature of the variable fuel,which temperature itself can be a control function.

The flow rate of the diluent when added to the variable fuel: Theaddition of diluent to the variable fuel can facilitate a wide varietyof changes to the variable fuel. For example, the heating value of thevariable fuel can be modified as discussed above. Further, volumetricand mass flow rates can impact the total amount of the variable fuelthat is needed (i.e., as a function of mass and heating value). Suchflow rates likewise can impact the pressure drop through the injectionnozzle as well as the fuel and jet speed through the nozzle. Theaddition flow rate for the diluent further can affect the peak flametemperature, which can impact the nature of any impurities that areformed (e.g., NOx and/or SOx), the extent of CO burnout that occurs, andthe CO₂ dissociation rate.

In one or more embodiments, variations in combustion properties causedby the varying chemistries of the variable fuel 207 a being input to thecombustor 220 can be normalized by controlling the oxidant 203 beinginput to the combustor. Preferably, the oxidant is a mixture of oxygenand a diluent (e.g., an inert gas, carbon dioxide, or water). Asillustrated in FIG. 2, a substantially pure stream of oxygen 203 isblended with a stream of substantially pure carbon dioxide 283 a forinput to the combustor 220. In some embodiments, the oxidant streamentering the combustor 220 can include about 5% to about 95% by massoxygen, about 5% to about 75% by mass oxygen, about 5% to about 50% bymass oxygen, about 10% to about 40% by mass oxygen, or about 15% toabout 30% by mass oxygen, with the remaining portion of the oxidantbeing the diluent. In particular exemplary embodiments, the mixture canbe about 20% by mass O₂ and about 80% by mass CO₂. In some cases, thediluent content in the oxidant can be a tuning parameter for any one ormore of combustion mass control, flame shape control, and flametemperature control. Diluent (e.g., CO₂) in some embodiments can beprovided in both the fuel stream and the oxidant stream. As such eitherstream (or both streams) can function as a moderator to ensure amoderate flame temperature for low NOx generation. In such combustionembodiments, about 1-2% molar excess oxygen can be provided into thecombustor to ensure complete fuel burnout. In some embodiments,combustion thus can be normalized by implementing a control functionthat can include varying a ratio of the oxygen to the carbon dioxide inthe oxidant as the composition of the variable fuel varies duringoperation of the power production process.

Normalizing combustion as the fuel chemistry of the variable fuelchanges during operation of the power production process can be achievedin further embodiments by adjusting further parameters related to thefuel and oxidant. In some embodiments, a control function forcontrolling combustion properties can include varying the temperature ofthe oxidant that is input to the combustor. Accordingly, as the fuelchemistry changes, the oxidant temperature may be adjusted to maintainone or more combustion properties within a defined, acceptable range. Insome embodiments, a control function for controlling combustionproperties can include varying the temperature of the variable fuel thatis input to the combustor. Accordingly, as the fuel chemistry changes,the fuel temperature may be adjusted to maintain one or more combustionproperties within a defined, acceptable range. In some embodiments, acontrol function for controlling combustion properties can includevarying the flow rate of the oxidant that is input to the combustor.Accordingly, as the fuel chemistry changes, the oxidant flow rate may beadjusted to maintain one or more combustion properties within a defined,acceptable range. In some embodiments, a control function forcontrolling combustion properties can include varying the flow rate ofthe variable fuel that is input to the combustor. Accordingly, as thefuel chemistry changes, the fuel flow rate may be adjusted to maintainone or more combustion properties within a defined, acceptable range.

In one or more embodiments, the varying chemistries of the variable fuel207 a being input to the combustor 220 can be normalized by beingblended with a further fuel of known, substantially consistentchemistry. The fuel of known, substantially constant or consistentchemistry can be characterized as a “normalizing fuel” in that it can beblended with the variable fuel in a sufficient ratio to dilute theeffects of changes in the chemistry of the variable fuel duringoperation of the power production process. For example, the normalizingfuel 207 b can be blended with the variable fuel 207 a at some pointupstream from the injection of the fuel(s) into the combustor 220. Theblend ratio, the temperature of the normalizing fuel, and similarproperties as already discussed herein can be utilized so that thenormalizing fuel 207 b can be controlled as a normalizing function thatcan be adjusted in one or more manners as the fuel chemistry of thevariable fuel 207 a changes during operation of the power productionprocess. Controlling this function can be effective to cause the flamegenerated in the combustion zone 221 of the combustor 220 by thecombustion of the combined fuel (variable fuel 207 a and normalizingfuel 207 b) can be substantially unchanged regardless of the actualchemistry of the variable fuel that is utilized for combustion. In someembodiments, the normalizing fuel can be natural gas or substantiallypure methane. In other embodiments, the normalizing fuel may be carbonmonoxide, hydrogen, or a syngas composition of substantially constant orconsistent chemistry. The normalizing fuel preferably will have a knownheating value so that the ratio of the normalizing fuel to the variablefuel can be varied during operation of the power production process asthe fuel chemistry of the variable fuel changes and thus maintainsubstantially constant combustion properties. In some embodiments, theratio of normalizing fuel to variable fuel can be about 0.1 to about 2,about 0.5 to about 1.5, or about 0.8 to about 1.2.

While normalizing of combustion may be achieved through one or more ofthe control functions described above, it is further possible to controlthe power production process downstream of combustion. In someembodiment, this can be achieved within the combustor 220. For example,the combustor 220 can be configured to include a combustion zone 221where the fuel and oxidant mix and the fuel is combusted and a dilutionzone 222 where the combustion product may undergo one or more changesprior to exiting the combustor. As illustrated in FIG. 2, the combustionzone 221 is upstream of the dilution zone 222, and the dilution zone isdownstream of the combustion zone. A diluent 283 c can be injected intothe combustor 220 in the dilution zone 222 to normalize one or moreproperties related to combustion. For example, the amount of diluent 283c can vary as the fuel chemistry of the variable fuel 207 a changesduring operation of the power production process to provide cooling tothe combustion exhaust as needed to maintain consistent combustionproperties. The amount of diluent 283 c that is added may also vary asthe flow rates of one or more of the variable fuel 207 a, the oxidant203, and the normalizing fuel 207 b (when applicable) changes. Thus, thediluent 283 c input to the dilution zone 222 can be used to make up forfluctuations in flow rates of one or more further streams as a means fornormalizing combustion.

In some embodiments, the input of a diluent into the dilution zone 222of the combustor 220 can be used as a control function for normalizationof combustion in a power production process in relation to a variety ofactions. In exemplary embodiments, it can be useful to control a massflow rate of the diluent injected into the combustor in the dilutionzone to be greater than a mass flow rate of the variable fuel providedto the combustor. In further exemplary embodiments, it can be useful tocontrol a mass flow rate of the diluent injected into the combustor inthe dilution zone to be greater than a mass flow rate of the oxidantprovided to the combustor. In other exemplary embodiments, it can beuseful to control a mass flow rate of the diluent injected into thecombustor in the dilution zone to be greater than a mass flow rate ofboth of the variable fuel provided to the combustor and the oxidantprovided to the combustor. In still further exemplary embodiments, itcan be useful to vary a temperature of the diluent injected into thecombustor in the dilution zone as the composition of the variable fuelvaries during operation of the power production process. The mass flowrate of the diluent injected into the dilution zone of the combustor mayremain substantially constant as the temperature is changed to make thenecessary adjustment based on the change in the fuel chemistry; however,the diluent flow rate into the dilution chamber may vary in combinationwith a change in the temperature of the diluent. In preferredembodiments, the diluent 283 c can be substantially pure carbon dioxide.In further embodiments, however, different diluents or combinations ofdiluents may be used. In some embodiments, the amount of diluent to beadded to the dilution zone can depend upon the length of the dilutionzone relative to the length of the combustion zone. For example, a ratioof the length of the combustion zone to a length of the dilution zonecan be about 0.25 to 1.5.

The ability to maintain a substantially constant combustor output acrossa variety of fuel chemistries can be important in that it allows for theuse of a single turbine in the power production system. Typically,changes in fuel chemistry can require changes to the turbine because ofthe differing characteristics of the combustor output based upon thefuel chemistry. As such, a power production plant must utilize multipleturbines (and typically multiple combustors) to accommodate differentfuel chemistries. Alternatively, a power production plant with a singlecombustor and/or single turbine can be limited to combustion of only asingle fuel chemistry that will leave little room for chemistryfluctuations. Because of the ability according to the present disclosureto provide a substantially constant combustor output across a variety ofdifferent fuel chemistries, it is possible to carry out the powerproduction methods with a power production system including only asingle turbine (and a single combustor). Accordingly, the presentmethods advantageously can normalize combustion properties across aspectrum of fuel chemistries so that a power production system andmethod designed to function under a defined set of operating parameterscan successfully function within the parameter set despite the use ofdiffering fuel chemistries that would otherwise be expected to causeoperating conditions to exceed one or more of the predefined operatingparameters. This can be particularly advantageous in that powerproduction can be achieved using differing fuel chemistries even withsystems and methods that typically have relatively narrow ranges ofallowable operating parameters, such as a semi-closed loop CO₂ cycle.Perturbations in combustion characteristics and flame across thesemixtures can be mitigated since performance of each individual fuelmixture composition can be made substantially identical throughimplementation of one or more of the control parameters.

Many modifications and other embodiments of the presently disclosedsubject matter will come to mind to one skilled in the art to which thissubject matter pertains having the benefit of the teachings presented inthe foregoing descriptions and the associated drawings. Therefore, it isto be understood that the present disclosure is not to be limited to thespecific embodiments described herein and that modifications and otherembodiments are intended to be included within the scope of the appendedclaims. Although specific terms are employed herein, they are used in ageneric and descriptive sense only and not for purposes of limitation.

The invention claimed is:
 1. A method for normalizing combustion in apower production process, the method comprising: providing a variablefuel to a combustor, the variable fuel having a composition that variesduring operation of the power production process; compressing thevariable fuel by a compressor to form a compressed fuel stream to beprovided to the combustor; providing a diluent into the combustor, thediluent comprises a first portion in a first conduit and a secondportion in a second conduit, wherein the first portion of the diluent isprovided to the combustor, and the second portion of the diluent iscombined with the compressed fuel stream to form a diluted compressedfuel stream to be provided to the combustor; combusting the variablefuel in the combustor with an oxidant to provide a combustor exhauststream; passing the combustor exhaust stream through a turbine togenerate power; and implementing at least one control function such thatone or both of a temperature and a mass flow of the combustor exhauststream exiting the combustor varies by no greater than 10% as thecomposition of the variable fuel varies during operation of the powerproduction process, wherein the at least one control function includes:controlling a mass flow rate of the diluent provided into the combustorto be greater than a mass flow rate of the variable fuel provided to thecombustor; controlling a mass flow rate of the diluent provided into thecombustor to be greater than a mass flow rate of the oxidant provided tothe combustor; or controlling a mass flow rate of the diluent providedinto the combustor to be greater than a mass flow rate of both of thevariable fuel provided to the combustor and the oxidant provided to thecombustor.
 2. The method of claim 1, wherein the variable fuel is asyngas, and wherein a ratio of carbon monoxide to hydrogen in the syngasvaries during operation of the power production process.
 3. The methodof claim 1, wherein the variable fuel is a mixture of methane, carbonmonoxide, and hydrogen, and a ratio between the methane, carbonmonoxide, and hydrogen varies during operation of the power productionprocess.
 4. The method of claim 1, wherein the oxidant is a mixture ofoxygen and the diluent.
 5. The method of claim 4, wherein the oxidantincludes 5% to 50% by mass oxygen, with the remaining portion of theoxidant being the diluent.
 6. The method of claim 4, wherein the oxidantincludes 15% to 30% by mass oxygen, with the remaining portion of theoxidant being the diluent.
 7. The method of claim 4, wherein the atleast one control function includes varying a ratio of the oxygen to thediluent in the oxidant as the composition of the variable fuel variesduring operation of the power production process.
 8. The method of claim1, wherein the at least one control function includes varying one ormore of a temperature of the oxidant input to the combustor, atemperature of the variable fuel input to the combustor, a flow rate ofthe oxidant input to the combustor, and a flow rate of the variable fuelinput to the combustor as the composition of the variable fuel variesduring operation of the power production process.
 9. The method of claim1, wherein the variable fuel provided to the combustor is blended with anormalizing fuel having a constant composition.
 10. The method of claim9, wherein the normalizing fuel is natural gas or pure methane.
 11. Themethod of claim 9, wherein the at least one control function includesvarying a ratio of the normalizing fuel to the variable fuel that iscombusted in the combustor.
 12. The method of claim 1, wherein thevariable fuel provided to the combustor is blended with the diluent. 13.The method of claim 12, wherein the diluent is carbon dioxide.
 14. Themethod of claim 12, wherein the at least one control function includesvarying a ratio of the diluent to the variable fuel that is combusted inthe combustor.
 15. The method of claim 1, wherein the combustor isconfigured with a combustion zone and a dilution zone, wherein thecombustion zone is upstream of the dilution zone, and the dilution zoneis downstream of the combustion zone, and wherein the diluent isinjected into the combustor in the dilution zone.
 16. The method ofclaim 15, wherein a ratio of the length of the combustion zone to alength of the dilution zone is 0.25 to 1.0.
 17. The method of claim 15,wherein the at least one control function includes varying one or moreof a temperature, a flow rate, and a chemistry of the diluent injectedinto the combustor in the dilution zone as the composition of thevariable fuel varies during operation of the power production process.18. The method of claim 1, wherein the diluent is carbon dioxide. 19.The method of claim 1, wherein the diluent provided into the combustoris provided separate from the variable fuel.
 20. The method of claim 1,wherein the diluent is provided into the combustor in a zone that isdifferent from a zone wherein one or both of the variable fuel and theoxidant is provided into the combustor.